1. Field of the Invention
The present invention relates generally to surface flaw inspection apparatuses for convex shaped bodies, and is directed more particularly to such inspection apparatus that avail positive and highly accurate, but still automatic inspections under a simple construction to check the existance or not of surface flaws on convex shaped bodies that have strong reflections (or have high reflectivity) on the surface thereof.
2. Description of the Prior Art
It is an extremely difficult problem to visually check the surface conditions (flaws there or not) on convex body surfaces with high reflectivity, for example, the convex surface of metal bodies that are mirror-finished or where such convex surface is plated. Therefore, in the recent years, various attempts are proposed as systems to automatically inspect whether or not there are such surface flaws as dirty, scratches or the like by photosensing such above described convex surfaces with high reflectivity by such image sensors such as a television camera or the like from which the image signal is electrically processed.
However, the fact remains that such above described flaw inspection on convex surfaces with high reflectivity is still extremely difficult, just like the case of visual inspection, by such presently proposed automatic inspection apparatuses for convex surfaces.
An example of such above described automatic inspection apparatus under the conventional art will be explained in reference with FIG. 1 and FIG. 2. FIG. 1 shows the relation between incident light IL and reflected light RL on the inspected surface which is a convex surface (spherical surface) 2 of a convex body 1 such as a ball, which is the inspected object. As well known, the incident light IL and reflected light RL on, for example, a point P on the convex surface 2, are symmetrical to each other with respect to the normal N to the convex surface 2 at point P. In other words, incident angle .theta..sub.I is equal to reflection angle .theta..sub.R.
FIG. 2 is a schematic diagram showing an example of a prior art inspection apparatus which will inspect the convex surface 2 of the convex body 1. On this figure, 3 designates a light source. The incident light IL from such light source 3 to the convex surface 2 of the convex body 1 is reflected on each of points A1, A2, A3 . . . on the convex surface 2 of the convex body 1 and then become reflected lights RL1, RL2, RL3 . . . . In the example on FIG. 2, due to the positions or locations of the light source 3 and a television camera 4, only the reflected light RL1 among the reflected lights is caught by the television camera 4 while the other reflected lights are out of the visual field of the television camera 4. In other words, out of the convex surface or inspected surface 2 of convex body 1, the flaws there or not can only be inspected at point A1. In this case, the reflected light RL1 that is introduced into camera 4, can be said to be the light from light source 3 itself, so that the reflected light RL1 is very strong or intensive which makes it extremely difficult to inspect small flaws at point A1.
Further, in order to totally inspect the inspected surface 2, it will be necessary to slowly rotate the convex body 1 relative to the camera 4 for a full or one rotation. In addition, since some of the other reflected lights on convex surface 2 at other points than A1 may also enter television camera 4, in the strict sense, it can be said that the conventional example on FIG. 2 may inspect surfaces other than point A1 at the same time, but as long as the inspected surface 2 is a convex surface, no matter how the positioning arrangements between the television camera 4 and the inspected surface 2 as well as the light source 3, are changed, the light beam itself from light source 3 will enter the camera 4 as an image such as in the case at point A1, which causes inspection difficulties.
FIG. 3 shows another prior art example which is proposed in order to avoid such above mentioned defective point. In this example, a plurality of, in the case shown in the figure, two light sources 3.sub.1 and 3.sub.2 are used to irradiate the convex surface 2 of the convex body 1 through light diffuser plates 5.sub.1 and 5.sub.2, and the television camera 4 placed therebetween is prevented from being directly irradiated upon by the lights from light sources 3.sub.1 and 3.sub.2 which are reflected on the convex surface 2 to thereby remove such conventional defect. In other words, with the example shown on FIG. 3, the light beams from light sources 3.sub.1, 3.sub.2 are diffused by light diffusers 5.sub.1 and 5.sub.2 to irradiate certain areas of the convex surface 2 and the lights reflected thereon are caught by the television camera 4 to inspect such areas of convex surface 2.
However, in this example, such a defect is caused that, as shown on FIG. 3, with respect to point B on the convex surface 2, the image of lens section 4 of the television camera 4 is picked up by the camera 4. In other words, by this prior art apparatus, the normal to point B on the convex surface 2 and the optical axis of the television camera 4 are coincident to each other so that the inspection of the point B on this convex surface 2 is impossible.
Symbol 6 on FIG. 2 and FIG. 3 indicates the inspection system to detect whether there is a flaw or not, such as scratches, etc. on the inspected surface 2 by processing the output image signal from the television camera 4, as well known.